Low loss oxide magnetic material

ABSTRACT

A low loss oxide magnetic material having low magnetic loss characteristic and being usable as the deflection yoke core for high speed scanning cathode ray tube, etc., which consists essentially of Fe 2  O 3 , MgO, ZnO and MnO as the principal constituents; and Bi 2  O 3  and CuO as the auxiliary constituents.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a magnetic material, and, more particularly,it is concerned with a low loss oxide magnetic material which is usableas a deflection yoke core for a high speed scanning cathode ray tube(hereinafter abbreviated as "CRT").

2. Discussion of Background

As the deflecting yoke core for CRT, there has long been used Mg-Mn-Znseries ferrite This material has been widely used both domestic andforeign as the standard ferrite material for the deflection yoke core,because it has high resistivity and hence vertical windings can bedirectly applied onto the core of such ferrite material with advantage.

On the other hand, owing to rapid diffusion in recent years of officeautomation (OA), computer-assisted-design (CAD),computer-assisted-manufacture (CAM), and so on, there is increasingdemand for CRT for graphic display, monitor display, etc which arerequired to have high resolution. These CRT's are required to have highperformance which is absent in the conventional CRT's for the householdtelevision sets, since such CRT's are scanned at high speed andtherefore have high horizontal deflection frequency On account of this,with the core for the deflection yoke wherein the winding system for thehorizontal and vertical windings, improvement in the convergenceproperties, etc. have been advanced energetically, the problems of theself-heat-generation of the core, and so on have become inegligible withincrease in the horizontal deflection frequency, and the reduction inloss of the core is the urgent task.

The Mg-Mn-Zn series ferrite which is used at present as the standardmaterial has been developed with a view to enabling the verticalwindings to be directly wound on and around the core. However, whilethis ferrite material has less vortex loss which occupies in the totalloss of the material because of its high resistance, the hysteresis lossthereof due to various influences such as composition of the material,crystal structure thereof, and various other factors is relativelygreat, the improvement of which has been the urgent task.

Therefore, when the core for the deflection yoke was manufactured with alow loss Mn-Zn series ferrite which is used as a main transformermaterial for the switching power source, etc., there could be observedthat the temperature rise in the deflection yoke core was fairlyimproved due to reduction in the core loss. However, the ringingphenomenon took place on the screen of the CRT. Thus, it has becomeapparent that adoption of this CRT is not possible from the point of itsimage quality.

This ringing phenomenon, when taking the horizontal winding as anexample, produces potential distribution between the adjacent layers ofthe windings, in case a voltage in the form of an impulse is introducedas an input, whereby capacity is generated between the adjacent scanninglines. Also, in general, when the frequency becomes higher, the floatingcapacity tends to increase. This can be inferred that there is broughtabout resonance between the component C of the capacity and thecomponent L of the windings, and the deflection current is subject tothe speed-modulation, with the result that there emerge on the screenthe brightness-modulated vertical stripes.

On the other hand, in the vertical winding, there is brought aboutdistributed capacity between the winding and the core at the result ofapplying the winding in the toroidal form directly on the core. Onaccount of this, there is formed a distribution circuit consisting ofdistribution of the electrostatic capacity between the winding and thecore, inductance of the winding, and resistance of the core. Thiscircuit is symmetrical in its left and right sides If the horizontalwinding is also symmetrical in its left and right sides, there should beno coupling of the horizontal winding with respect to the inductance ofthis circuit. If, however, there exists a certain asymmetry, there takesplace coupling with the current flowing through the horizontal windingwith the consequence that vibrating current flows locally in and throughthe vertical winding.

According to analyses done by the present inventor, it has been foundthat this vibrating current becomes increased, as the resistivitybecomes smaller, and that the critical resistance is 10⁴ ohm-m. It goeswithout saying that the greater this value is, the more is it desirable.

From such standpoint, there has been proposed a low loss oxide magneticmaterial, while still retaining its high resistance. Such material isNi-Cu-Mn-Zn series ferrite, which has attained its low loss which isapproximately half that of the conventional Mg-Mn-Zn series ferrite andis utilized as the ferrite for the high speed scanning deflection yokein a frequency range of from 64 KHz to 90 KHz.

However, the conventional low loss oxide magnetic material of theabovementioned composition contains therein nickel (Ni) which isexpensive and is rare in the natural resources, on account of whichthere was a problem such that disadvantage in the aspect of itsmanufacturing cost could not be avoided.

SUMMARY OF THE INVENTION

The present invention has been made with a view to solving the points ofproblem as mentioned in the foregoing, and aims at providing a low lossoxide magnetic material which is capable of reducing theself-heat-generation of the core by increasing its deflection frequency,is capable of suppressing the ringing phenomenon which is liable tobring about deterioration in the image quality, and is susceptible ofbeing used as the deflection yoke core for a high resolution CRT, etc..

According to the present invention, there is provided a low loss oxidemagnetic material which consists essentially of, as the principalcomponents, 43 to 47 mol % of Fe₂ O₃, 27 to 35 mol % of MgO, 13 to 20mol % of ZnO and 3 to 10 Mol % of MnO; and, as the auxiliary components,0 to 1.5 % by weight of Bi₂ O₃ and 0 to 1.5% by weight of CuO.

The foregoing object, other objects as well as specific construction andproperties of the magnetic material according to the present inventionwill become more apparent and understandable from the following detaileddescription thereof, when read in conjunction with the accompanyingdrawing illustrating a couple of preferred examples according to thepresent invention.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING

In the drawing:

FIG. 1 is a graphical representation showing a relationship between theadding quantity of Bi₂ O₃ and the electric power loss;

FIG. 2 is a graphical representation showing changes in the power loss,when Bi₂ O₃ and CuO are added in combination;

FIG. 3 is a graphical representation showing the power loss versustemperature characteristics, when 0.5% by weight of Bi₂ O₃ and 1.0 % byweight of CuO are added in combination; and

FIG. 4 is a graphical representation showing the power loss versusfrequency relationship of the same test specimens as shown in FIG. 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following, the present invention will be described in detail withreference to preferred embodiments thereof.

The low loss oxide magnetic material according to the present inventioncan be obtained by adding to an Mg-Mn-Zn series ferrite at least oneelement which is capable of reducing the power loss thereof withoutdecreasing its specific resistance.

Such magnetic material has low power loss, while maintaining highspecific resistance, so that it is able to suppress self-heat-generationof the deflection yoke core, to increase operating reliability of thedeflection yoke, and, at the same time, is capable of reducing theringing phenomenon which has been the main factor of deterioration inthe quality of image on the CRT.

With a view to enabling those persons skilled in the art to put thepresent invention into practice, the following examples are presented.

EXAMPLE 1

Starting materials were weighed so as to obtain a composition consistingof 45.0 mol % of Fe₂ O₃, 31.0 mol % of MgO, 7.0 mol % of MnO and 17.0mol % of ZnO.

The powder mixture of these starting materials was calcined for one hourat a temperature of 850° C., followed by pulverizing the calcinedmaterial in a ball mill for four hours, thereby obtaining a testmaterial.

Subsequently, Bi₂ O₃ was added to this test material in a quantityranging from 0 to 1.5 % by weight as shown in Table 1 below, and thematerial added with differing quantities of Bi₂ O₃ were uniformly mixedby means of a crush-mixer. Thereafter, polyvinyl alcohol solution wasadded in a quantity of 10 % by weight with respect to the ferrite powderso as to granulate the material, which was then shaped into annular testspecimens under a pressure of 1 ton/cm².

These test specimens were sintered in the atmosphere for two hours at atemperature of l,250° C., and the thus obtained annular test specimenswere measured for their electro-magnetic properties with the resultsbeing shown in Table 1 below as well as in FIG. 1.

                                      TABLE 1                                     __________________________________________________________________________                    Power Loss                                                    Bi.sub.2 O.sub.3                                                                  μi tan δ/μi                                                                   (16 KHz, 1000 Gauss)                                                                        Resistivity                                     (wt %)                                                                            (100 KHz)                                                                           (11 KHz)                                                                            20° C.                                                                        100° C.                                                                       (Ω · m)                          __________________________________________________________________________    0   348   5.7 × 1.sup.-5                                                                182 mW/cm.sup.3                                                                      112 mW/cm.sup.3                                                                      9.9 × 10.sup.6                            0.1 410   5.6 × 10.sup.-5                                                               165    97     9.3 × 10.sup.6                            0.2 430   5.6 × 10.sup.-5                                                               158    86     9.0 × 10.sup.6                            0.3 453   5.5 × 10.sup.-5                                                               145    79     8.7 × 10.sup.6                            0.5 486   5.1 × 10.sup.-5                                                               140    75     8.5 × 10.sup.6                            0.7 487   5.1 × 10.sup.-5                                                               138    79     8.1 × 10.sup.6                            1.0 482   5.3 × 10.sup.-5                                                               136    80     7.9 × 10.sup.6                            1.2 475   5.4 × 10.sup.-5                                                               133    82     7.3 × 10.sup.6                            1.5 477   5.5 × 10.sup.-5                                                               135    85     6.5 × 10.sup.6                            __________________________________________________________________________

From the above tabulated test results, it is seen that the addition ofBi2O3 remarkably improves the power loss, while maintaining the specificresistance without its substantial change.

EXAMPLE 2

Starting materials were weighed so as to obtain a composition consistingof 45.0 mol % of Fe₂ O₃, 31.0 mol % of MgO, 7.0 mol % of MnO, and 17.0ml % of ZnO.

The powder mixture of these starting materials was calcined for one hourat a temperature of 850° C., followed by pulverizing the calcinedmaterial in a ball mill for four hours, thereby obtaining a testmaterial.

Subsequently, Bi₂ O₃ and CuO were added to this test material in aquantity as shown in Table 2 below, and the material added withdiffering quantities of Bi₂ O₃ and CuO were uniformly mixed by means ofa crush-mixer. Thereafter, polyvinyl alcohol solution was added in aquantity of 10 % by weight with respect to the ferrite powder togranulate the material, which was then shaped into annular testspecimens under a pressure of 1 ton/cm².

These test specimens were sintered in the atmosphere for two hours at atemperature of 1,250° C., and the thus obtained annular test specimenswere measured for their electro-magnetic characteristics with theresults being shown in Table 2 below as well as in FIGS. 2 to 4.

                                      TABLE 2                                     __________________________________________________________________________                         Power Loss                                               BiO.sub.3                                                                         CuO μi tan δ/μi                                                                    (16 KHz, 1000 Gauss)                                                                        Resistivity                                (wt %)                                                                            (wt %)                                                                            (100 KHz)                                                                           (100 KHz)                                                                            20° C.                                                                        100° C.                                                                       (Ω · m)                     __________________________________________________________________________    0   0   348    5.7 × 10.sup.-5                                                               182 mW/cm.sup.3                                                                      112 mW/cm.sup.3                                                                      9.9 × 10.sup.6                       0.3 0.2 425    6.6 × 10.sup.-5                                                               137    82     9.4 × 10.sup.6                           0.5 398    8.0 × 10.sup.-5                                                               130    76     9.1 × 10.sup.6                           1.0 337   11.7 × 10.sup.-5                                                               122    71     8.7 × 10.sup.6                           1.5 286   16.5 × 10.sup.-5                                                               125    76     8.5 × 10.sup.6                       0.5 0.2 446    6.4 × 10.sup.-5                                                               133    78     8.3 × 10.sup.6                           0.5 418    7.8 × 10.sup.-5                                                               122    77     8.1 × 10.sup.6                           1.0 353   11.8 × 10.sup.-5                                                               118    68     7.9 ×  10.sup.6                          1.5 319   16.1 × 10.sup.-5                                                               116    77     7.6 × 10.sup.6                       1.0 0.2 452    6.7 × 10.sup.-5                                                               146    87     6.5 × 10.sup.6                           0.5 423    8.2 × 10.sup.-5                                                               140    82     6.0 × 10.sup.6                           1.0 348   12.5 × 10.sup.-5                                                               135    75     5.5 × 10.sup.6                           1.5 360   17.2 × 10.sup.-5                                                               129    78     4.9 × 10.sup.6                       __________________________________________________________________________

From the above tabulated test results, it is seen that, by addition ofBi₂ O₃ and CuO in combination, the power loss of the material is furtherimproved.

By the way, FIG. 1 is a graphical representation showing a relationshipbetween the adding quantity of Bi₂ O₃ and the electric power loss, whileFIG. 2 is a graphical representation showing changes in the power loss,when Bi₂ O₃ and CuO are added in combination, the measuring conditionsfor both FIGS. 1 and 2 being 16 KHz, 1,000 Gausses and 100° C.

FIG. 3 is a graphical representation showing the power loss versustemperature characteristics, when 0.5% by weight of Bi₂ O₃ and 1.0% byweight of CuO are added in combination, wherein the measuring conditionsare 16 KHz and 1,000 Gausses.

FIG. 4 is a graphical representation showing the power loss versusfrequency relationship of the same test specimens as shown in FIG. 3,wherein the measuring conditions are 1,000 Gausses and 100° C.

From the above results, the adding quantity of Bi₂ O₃ is upto andincluding 1.5 % by weight, in excess of which the power loss of thematerial would increase badly to thereby bring about inconvenience suchthat cracks and other defects would occur in the sintered articles Inthe same way, the adding quantity of CuO is also upto 1.5% by weight.

By the way, in the foregoing examples of the present invention, use wasmade of oxides as the material for the ferrite and the additives. Itgoes without saying, however, that similar effect can be obtained withuse of those compounds such as carbonates, etc. which are decomposedinto oxides upon heating.

The magnetic material according to the present invention finds its usenot only in the deflecting yoke, but also in other uses wherein it isplaced in high magnetic flux with accompaniment of high heat generation.

As described in the foregoing, the present invention makes it possibleto remarkably improve the power loss of the Mg-Mn-Zn series ferrite byaddition thereto of those additives such as Bi₂ O₃, CuO, and otherswithout giving influence on the specific resistance of the material,which is of consequence in respect of the characteristic property as thedeflection yoke core. On account of this, it becomes possible tosuppress heat generation of the deflection yoke, etc., wherebyimprovement in the operating reliability, miniaturization, and reducedweight of the part can be realized.

Although, in the foregoing, the present invention has been describedwith reference to specific examples thereof, the invention is notrestricted to these examples alone, but any changes and modificationsmay be made by those persons skilled in the art within the spirit andscope of the invention as recited in the appended claims.

What is claimed is:
 1. A ferrite magnetic material exhibiting low powerloss for use as a deflector yoke core for a high speed scanning cathoderay tube, consisting essentially of 43-47 mol % of Fe₂ O₃, 27-35 mol %of MgO, 13-20 mol % of ZnO, 3-10 mol % of MnO, from about 0.1 to 1.5 wt.% of Bi₂ O₃ and CuO in an amount of from about 0.2 to 1.5 wt. %.
 2. Aferrite magnetic material exhibiting low power loss for use as adeflector yoke core for a high speed scanning cathode ray tube,consisting essentially of 43-47 mol % of Fe₂ O₃, 27-35 mol % of MgO,13-20 mol % of ZnO, 3-10 mol % of MnO, from about 0.1-1.0 wt. % of Bi₂O₃ and CuO in an amount from about 0.2-1.5 wt. %.